Loss of WHY1 has Specific Effects on C/N Metabolism
Several transcripts associated with primary metabolic pathways were differentially abundant in the basal portion of wild type and WHY1 knockdown leaves (Fig. 8A). Significant differences were observed in transcripts encoding enzymes associated with the Calvin cycle, starch and sugar metabolism, glycolysis, the TCA cycle and amino acid metabolism. Many of these transcripts were more abundant in WHY1 knockdown than wild type leaves although transcripts encoding hexokinase (MLOC_54094.1), β-amylase (AK368826) a methionine S-methyltransferase (AK368357), an O-acetylcysteine thiol-lyase (AK248898.1) and an arginase (MLOC_65968.1) were consistently less abundant in WHY1 knockdown lines.
Differences in transcript abundance were reflected by significant differences in primary metabolic profiles (Fig. 8B). Twenty-two of 71 polar compounds analysed by GC/MS were significantly differentially abundant in wild type and WHY1 knockdown leaf basal regions. Eight of these compounds were unidentified with the remainder comprising primarily organic and amino acids. All of the TCA cycle components detected were significantly lower in WHY1 knockdown leaves than in wild type leaves as was the non-proteinaceous amino acid γ-amino butyric acid (GABA) that functions as a cytosolic bypass of specific steps (Sweetlove, Beard, Nunes-Nesi, Fernie, & Ratcliffe, 2010). Similarly, serine and aspartate were present at lower concentrations in WHY1 knockdown leaves while glycine, valine, leucine, threonine and isoleucine were present at higher concentrations, particularly in W1-7 (Fig. 8B).